The short answer
Joining keeps your personal credits and does not transfer them into the team pool. A pool charge does not reduce your personal balance. Its existing renewal and validity rules continue, so joining does not extend its validity. Personally purchased extra credits do not automatically become team credits either. Your personal subscription continues independently until you change or cancel it separately. While the team pool is active, the sidebar shows the team pool instead of your personal balance. This is intended: the pool is what your requests are charged to. You still find your personal balance under Billing, and the sidebar shows it again after you leave the team. If you own a team with your own Professional or Enterprise subscription, only the team pool renews monthly. You receive no additional 30 personal credits. Previously granted personal monthly credits remain valid until their period ends. Purchased and bonus credits remain available. Invited members keep the allowance of their own plan. Without a team, your paid plan allowance remains personal.